使用子查询中的别名

Question

我想使用子查询中的别名。

Fruit table: 
name: is_bio: from_id: to_id: 
Apple yes  Spain  Italy 

Country table: 
id:  packaging_type: packaging_quantity: 
Italy wood box   12 
Spain paper box   18 

而且我想是这样的：

with subquery as (SELECT a.packaging_type, a.packaging_quantity, b.packaging_type, b.packaging_quantity 
FROM fruit 
    inner join country a on a.country.id = fruit.from_id 
    inner join country b on b.country.id = fruit.to_id 
WHERE fruit.name = 'Apple') 
SELECT a.packaging_quantity from subquery; 

但我得到了一个错误：

ORA-00904: "A"."PACKAGING_QUANTITY": invalid identifier 
00904. 00000 - "%s: invalid identifier" 
*Cause:  
*Action: 
Error at Line: 7 Column: 14 

Answer 1

这个答案的原始版本。

您的CTE有四列，但只有两列别名packaging_type和packaging_quantity。表别名不是完全限定的列名称（即包括别名或表名称），而只是列名称本身。

你需要给他们使用as不同的名称，如：

with subquery as (
     select a.packaging_type as packaging_type_a, 
      a.packaging_quantity as packaging_quantity_a, 
      b.packaging_type as packaging_type_b, 
      b.packaging_quantity as packaging_quantity_b 
     from fruit inner join 
      country a 
      on a.country.id = fruit.from_id inner join 
      country b 
      on b.country.id = fruit.to_id 
     where fruit.name = 'Apple' 
    ) 
select packaging_quantity_a 
from subquery;